Caliche may have about 20 per cent sodium nitrate and 25 per cent sodium chloride. Now if we look at Fig. 5 we see that one method of treatment would be to leach the ore at a temperature of 80°C. At this point we would dissolve 118 parts of sodium nitrate and 13 parts of sodium chloride per 100 parts of water. Now by cooling this
a col $1 x
s | $ Y
0 A <&/
A a H 10 P4I dl <P
§1 % y
on fcl f"
100 Parts Salts per 100 pts.\Vatec
FIG. 4.—Effect of another salt on solubility.
solution to 20°C. the solution would hold 26 parts sodium nitrate or 118 — 26 = 92 parts, sodium nitrate will be precipitated and as sodium chloride is more soluble at 20°C. than at 80°C. no salt would be precipitated. Therefore theoretically we should get 100 per cent sodium nitrate. Due to the problem of getting water in Chile and
10 20 30 40
Parts per 100 pts.Water
FIG. 5.—Sodium sulphate-sodium nitrate solubilities.
fuel expense this process is peculiarly useful as the salt and weak nitre solution may now be used for dissolving additional niter with no evaporation, except that required to concentrate wash liquors.
Permeable Membranes as Applied to Selective Dissolution.—In most of the leaching and dissolution processes the material is shredded or ground so as to